Rocket Propelled Grenades (RPGs) have been employed since World War II against armored vehicles and fortifications. They are cheap, effective, and difficult to counter. Currently, millions of these weapons are used by insurgent and guerilla forces, as well as regular forces in many countries. RPGs can penetrate as much as a foot of steel armor, so it is not practical to use steel for RPG protection on most vehicles because of the weight. To provide at least partial protection against these weapons, bar or slat armor has been developed, and is in use on a number of military vehicles. Bar armor works by exploiting a design feature in the RPG, namely that causing the inner and outer ogives (the hollow conical forward members of the RPG warhead) to become electrically connected causes the piezoelectric nose element to become short circuited, thus denying electrical power to the initiating element at the rear of the RPG. When an RPG passes between the bars of bar armor at high speed without the forward nose element hitting a bar, the outer ogive is crushed into the inner ogive, a short circuit is established, and the RPG is dudded. Bar and slat armor is much lighter than steel would be, but is still relatively heavy when applied to large areas of an armored vehicle, adding hundreds or even thousands of pounds. For many applications, lighter solutions are desired, as well as improved effectiveness and visibility through the bars.
Currently, bar armor is typically composed of aluminum bars 30 to 40 inches long, each separated by about 3 inches, with a square cross section about ½ inch on a side. Slat armor is similar but with a cross section more typically ¼ inch across by 1 or 2 inches in depth. With low cost materials, these dimensions cannot easily be reduced because the resultant low lateral strength allows the bars or slats to be pushed apart by the RPG ogive without inflicting sufficient damage. However, it would be possible to reduce these dimensions if the bars could be constrained laterally without introducing structural members that could themselves provide sufficient impact to the piezoelectric element to set off the RPG.